Liquid crystal display device, recognized as a low-power-consumption, space-saving image display device, has been expanding its applications year by year. As the market expands, not only within television or the like where high-definition image is required, but also into mobile devices including mobile phone and tablet personal computer, there has been an increasing need for thinning. The liquid crystal display device is configured by a liquid crystal cell, and polarizing plates disposed on both sides thereof. In many cases, the polarizing plate is optically compensated while laminated with a retardation film.
Patent Document 1 describes an optical sheet which includes a retardation film having an Nz value exceeding 0.4 and less than 0.6, and (nx−ny)d of 200 to 350 nm, and a transparent layer formed on one surface thereof, having a thickness of 10 μm or less, and a refractive index anisotropy given by nx≈ny>nz, where nz is refractive index observed in the thicknesswise direction defined as the Z axis, nx is refractive index observed in one direction in a plane normal to the Z axis, ny is refractive index observed in the direction normal to the Z axis and the X axis, the X axis is laid in the direction in plane along which the refractive index appears maximum, Nz=(nx−nz)/(nx−ny) holds, and d is the film thickness.
Patent Document 2 describes a composite retardation plate configured by using one or two or more sheets of a retardation film having at least one of nx, ny and nz being different from the other, where nx and ny being in-plane principal refractive indices, nz being refractive index in the thicknesswise direction, nx≧ny holds; and one or two or more sheets of liquid crystal phase sheet which is composed of a transparent base having different values of nx, ny and nz, and a liquid crystal polymer layer provided thereto; wherein the sheets are combined so that the retardation film, the transparent base and the liquid crystal polymer layer will have different wavelength dependence of birefringence, the retardation film and the transparent base will have different values of Nz which is defined by (nx−nz)/(nx−ny); and each of the retardation film and the transparent base is composed of a film having a non-liquid crystalline polymer aligned therein.
Patent Document 3 describes a light absorption anisotropic film containing at least one species of thermotropic liquid crystalline dichroic dye, and at least one species of thermotropic liquid crystalline polymer, wherein the mass content of the thermotropic liquid crystalline dichroic dye in the light absorption anisotropic film is 30% or more.